This invention relates in general to a laser printer and more particularly relates to a vacuum drum fabricated from an aluminum foam core.
Pre-press color proofing is a procedure used by the printing industry to create representative images of printed material. This procedure avoids the high cost and time required to produce printing plates and set-up a high-speed, high-volume printing press to produce a single intended image for proofing prior to a production run of the intended image. In the absence of pre-press proofing, a production run may require several corrections to the intended image to satisfy customer requirements, and each of the intended images would require a new set of printing plates. By utilizing pre-press color proofing, time and money are saved.
A laser thermal printer having half-tone color proofing capabilities is disclosed in commonly assigned U.S. Pat. No. 5,268,708 titled xe2x80x9cLaser Thermal Printer With An Automatic Material Supply,xe2x80x9d issued Dec. 7, 1993 in the name of R. Jack Harshbarger, et al. The Harshbarger, et al. device is capable of forming an image on a sheet of thermal print media by transferring dye from dye donor material to thermal print media. This is achieved by applying thermal energy to the dye donor material to form an image on the thermal print media. This apparatus comprises a material supply assembly; a lathe bed scanning subsystem, which includes a lathe bed scanning frame, a translation drive, a translation stage member, a laser printhead; a rotatable vacuum imaging drum; and exit transports for the thermal print media and dye donor material.
The Harshbarger, et al. apparatus meters a length of the thermal print media in roll form from a material supply assembly. The thermal print media is measured and cut into sheets of the required length, transported to the vacuum imaging drum, and wrapped around and secured to the vacuum imaging drum. A length of dye donor roll material is metered out of the material supply ssembly, measured, and cut into sheets of the required length. The cut sheet of dye donor roll material is transported to and wrapped around the vacuum imaging drum, and superposed in registration with the thermal print media. The scanning subsystem traverses the printhead axially along the rotating vacuum imaging drum to produce the image on the thermal print media. The image is written in a single swath, traced out in a continuous spiral, concentric with the imaging drum, as the printhead is moved parallel to the drum axis.
Although the printer disclosed in the Harshbarger, et al. performs well, there is a long-felt need to reduce manufacturing costs for this type of printer and for similar types of imaging apparatus. In particular, improvements which would lower the cost and complexity of the vacuum imaging drum would be advantageous for reducing overall system cost and improving long-term equipment performance.
The imaging drum disclosed in Harshbarger, et al. is constructed using a hollow, machined vacuum drum, finished and assembled as disclosed in U. S. Pat. Nos. 5,964,133, 5,376,954, 5,276,464 and 6,002,419. Considerable assembly time and cost are involved in fabricating the imaging drum and in balancing the drum to allow proper rotation at the high speeds used during imaging. Drum weight in excess of 30 lbs. is a significant factor in the design of the supporting chassis structure, which is a machined casting in the apparatus disclosed in Harshbarger, et al. The inertia of the heavy drum adversely impact system throughput, since time is needed to accelerate the drum to writing speed and to slow the drum to a stop to unload media after writing. Additionally, the mass of the drum wall causes some distortion, which may be due to uneven vacuum distribution, as is noted in U.S. Pat. No. 5,183,252 (Wolber et al.)
Substitution of lighter metals for an imaging drum can reduce the weight of the drum, but present other problems such as higher materials cost, lower resistance to oxidation and corrosion, and reduced structural strength. Aluminum foam core material has been used in aeronautical, heat exchange, and other applications due to its light weight and favorable thermal response properties. However, perhaps because conventional foam core material lacks a finished surface, this material has not been employed for imaging drum fabrication.
There has been a long-felt need to reduce the cost, complexity, and weight of a vacuum imaging drum without compromising dimensional stability and performance. However, up to this time, conventional imaging drum solutions have been limited to the use of conventional machined tubing.
It is the object of the present invention to provide a lightweight vacuum imaging drum for an image processing system and a method for producing such an imaging drum.
According to one aspect of the present invention, an aluminum foam core vacuum imaging drum is comprised of an aluminum foam cylinder having a densified surface. A first metal layer covers the densified surface, and vacuum holes in the first metal layer connect a surface of the first metal layer to an interior of the aluminum foam cylinder. In one embodiment, the aluminum foam cylinder is fabricated using open-cell aluminum foam core construction.
According to an embodiment of the present invention, a vacuum imaging drum is fabricated from a cylindrical core of open-cell aluminum foam core material. End plates are pressed into place on the top and bottom sides of the cylindrical core for bearings and mounting. The outer surface of the cylindrical core is compacted for increased density, then covered with a uniform metal coating. The surface of the drum is be machined to provide the appropriate arrangement of orifices for providing a hold-down vacuum for thermal and dye donor media.
An advantage of the present invention is that a lightweight imaging drum is produced. This simplifies the design of support components for starting and stopping the drum and reduces the amount of structural support required from a print engine chassis and frame assembly. A further advantage of lightweight construction is that it simplifies the task of balancing the drum for high-speed operation.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.